Iron exists in a large quantity that is second most common in the crust after Aluminum and is mainly cast in steel to be used as a material for various structures, ships, automobiles and various mechanical devices. Iron is not found in the form of pure iron. Starting off from iron hematite, magnetite, calcite, siderite and the like which contain mainly iron, as a raw material, they are roasted to be made into iron oxide. Then, limestone is added as a fusing agent and coke is added as a reducing agent and hot air is blown within a blast furnace, and the coke is burned and at the same time an ore is reduced to be made into iron, and melted to produce pig iron. Meanwhile, to make pure iron from pig iron and a steel scrap, a method of electrolytic refining in an aqueous solution of iron salt with the pig iron and steel scrap as electrodes is used.
As an example of an electrolytic reduction process, there is a method for producing a metal by electrolytic reduction of a feedstock including an oxide of a first metal. The method includes, disposing the feedstock in a state contacting a cathode and a molten salt, disposing an anode within an electrolytic cell in a state contacting the molten salt, and applying a potential between the anode and the cathode to remove oxygen from the feedstock. The anode is a second metal that is a molten metal at an electrolytic temperature in the cell. The second metal is a metal different from the first metal. Oxygen removed from the feedstock upon electrolysis reacts with the molten second metal to form an oxide including the second metal. Therefore, oxygen is not released as a gas at the molten anode (Patent Document 1).
In the method for producing a metal by electrolytic reduction of a feedstock including a metal oxide, iron is obtained from a cathode by using sulfuric acid or hydrochloric acid as an electrolytic solution. Therefore, a problem arises wherein it is difficult to control the purity of the iron due to hydrogen bubbles formed by hydrogen overvoltage during the electrolysis process. Also, there is a problem of increase in costs for the process because the voltage of the electrolytic cell is as very high, as high as 3V, and the power consumption is also high.
Further, as an electrolytic refining method, a metal oxide recovery method includes, preparing a raw material containing titanium and iron, putting the raw material into a refining vessel, putting a molten iron is into the refining vessel, and blowing a gas containing oxygen into the refining vessel. In the process of blowing the gas, the titanium contained in the raw material may be made to be contained in the form of titanium oxide in a slag which is formed when the molten iron is refined (Patent Document 2).
Although the above method discloses a method of recovering valuable metals by electrolytic refining an iron ore containing iron as an iron source, there is a problem that the metal is recovered in an oxide form, so it is difficult to obtain pure iron.
Iron collected by electrolytic refining has very good magnetic properties, and the demand for vacuum tubes and high-performance magnetic materials in addition to catalysts, electromagnetic materials and alloy materials is continuously increasing. Therefore, there still remains a necessity for developing a more efficient method for producing a mass amount of reduced iron using electrolytic refining with a simpler process.